From: Steve Baird <ba...@adacore.com> A recent change to reduce duplication of compiler-generated Put_Image and streaming subprograms introduced some regressions. The fix for one of them was incomplete.
gcc/ada/ * exp_attr.adb (Build_And_Insert_Type_Attr_Subp): Further tweaking of the point where a compiler-generated Put_Image or streaming subprogram is to be inserted in the tree. If one such subprogram calls another (as is often the case with, for example, Put_Image procedures for composite type and for a component type thereof), then we want to avoid use-before-definition problems that can result from inserting the caller ahead of the callee. Tested on x86_64-pc-linux-gnu, committed on master. --- gcc/ada/exp_attr.adb | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) diff --git a/gcc/ada/exp_attr.adb b/gcc/ada/exp_attr.adb index e12e8b4a439..03bf4cf329c 100644 --- a/gcc/ada/exp_attr.adb +++ b/gcc/ada/exp_attr.adb @@ -1954,6 +1954,44 @@ package body Exp_Attr is while Present (Ancestor) loop if Is_List_Member (Ancestor) then Insertion_Point := First (List_Containing (Ancestor)); + + -- A hazard to avoid here is use-before-definition + -- errors that can result when we have two of these + -- subprograms where one calls the other (e.g., given + -- Put_Image procedures for a composite type and + -- for a component type, the former will often call + -- the latter). At the time a subprogram is inserted, + -- we know that the one and only call to it is + -- somewhere in the subtree rooted at Ancestor. + -- So that placement constraint is easy to satisfy. + -- But if we construct another subprogram later and + -- if that second subprogram calls the first one, + -- then we need to be careful not to place the + -- second one ahead of the first one. That is the goal + -- of this loop. This may need to be revised if it turns + -- out that other stuff is being inserted on the list, + -- so that the loop terminates too early. + + -- On the other hand, it seems like inserting things + -- earlier offers more opportunities for sharing. + -- If Ancestor occurs in the statement list of a + -- subprogram body (ignore the HSS node for now), + -- then perhaps we should look for an insertion site + -- in the decl list of the subprogram body and only + -- look in the statement list if the decl list is empty. + -- Similarly if Ancestor occors in the private decls list + -- for a package spec that has a non-empty visible + -- decls list. No examples where this would result in more + -- sharing and less duplication have been observed, so this + -- is just speculation. + + while Insertion_Point /= Ancestor + and then Nkind (Insertion_Point) = N_Subprogram_Body + and then not Comes_From_Source (Insertion_Point) + loop + Next (Insertion_Point); + end loop; + pragma Assert (Present (Insertion_Point)); end if; Ancestor := Parent (Ancestor); -- 2.43.2